In recent years, as the technology for visualizing brain has been developed, not only fully realizing physiological knowledge about the brain but also assuming a state of a human from a brain measuring signal is performed.
Examples of a method for measuring a brain activity in a non-invasive manner include electroencephalogram measurement, functional magnetic resonance imaging (fMRI), magnetoencephalography, and near-infrared spectroscopy (NIRS).
As a background technology of the technological field, there is JP-A-2011-150408 (PTL 1). The application describes “In a work place where machines are used, a machine learning algorithm is employed to estimate an internal state (visual caution, working memory, a degree of skill or the like) which is obtained from a biometric signal of an operator. In addition, in a case of predicting and detecting a state where a human error is likely to occur, and estimating a state where a risk of making a mistake is high, the mistakes are prevented in advance by feeding back the state to the operator by means of the sense of sight, the sense of hearing, and the sense of touch or by a combination of the senses (refer to summary).